With the recent development of an Internet related art, it becomes possible to provide on the internet several kinds of services such as music on demand. In such a service, the transmission capacity of downlink channel is greatly increased. It is largely expected that high speed transmission in the downlink channel is to be achieved in order to realize services with large transmission capacity of the downlink channel. In addition, several technology developments are undergone on high speed transmission in downlink channel. As one technology of high speed transmission in downlink channel, a modulation method is adaptively updated in the transmission side, an adaptive modulation communication system carries out data transmission with a preferable efficiency.
A conventional adaptive modular ion communication system will be explained with reference to FIG. 1. FIG. 1 is a block diagram shows a conventional communication apparatus.
Communication apparatus 10 receives a radio signal in radio reception section 12 via antenna 11. Predetermined radio reception processing are performed on the received signal in radio reception section 12. The radio reception processed signal is outputted to demodulator 13. The data is demodulated in demodulator 13, and it is separated into a reception data and estimation value of the reception signal estimated in reception quality estimating section 61 of the receiving side to be described later using FIG. 5. Channel quality estimating section 14 estimates the channel quality from the estimation value of the separated quality of reception signal and outputs the result to transmission method determining section 15.
Transmission method determining section 15 determines transmission method of a signal transmitted to a communication partner from channel quality and outputs the result to switch 16, switch 17 and modulator 18. Here, An appropriate modulation technique is chosen among BPSK (Binary Phase Shift Keying), QPSK, 8PSK, 16QAM (sixteen Quadrature Amplitude Modulation), 64QAM (sixty four Quadrature Amplitude Modulation) modulation as a transmission method.
Switch 16 outputs the transmission data to either BPSK modulator 19, QPSK modulator 20, 8PSK modulator 21, 16QAM modulator 22, or 64QAM modulator 23 based on the transmission method determined in transmission method determining section 15.
BPSK modulator 19 performs phase modulation on the transmitting data so that 1 symbol corresponds to 1 bit (2 values) of information and outputs the result to switch 17. QPSK modulator 20 performs phase modulation on the transmitting data so that 1 symbol corresponds to 2 bits (4 values) of information and outputs the result to switch 17. 8PSK modulator 21 performs phase modulation on the transmitting data so that 1 symbol corresponds to 3 bits (8 values) of information and outputs the result to switch 17.
16QAM modulator 22 performs multi-level orthogonal amplitude modulation on the transmitting data so that 1 symbol corresponds to 4 bits (16 values) of information and outputs the result to switch 17. 64QAM modulator 23 performs multi-level orthogonal amplitude modulation on the transmitting data so that 1 symbol corresponds to 6 bits (64 values) of information and outputs the result to switch 17.
Switch 17 outputs the transmitting data which is modulated in either BPSK modulator 19, QPSK modulator 20, 8PSK modulator 21, 16QAM modulator 22 or 64QAM modulator based on a transmission method determined in transmission method determining section 15 to multiplexer 24.
Multiplexer 24 multiplexes the modulated transmitting data and the information of transmission method determined in transmission method determining section 15 and outputs the result as a transmission signal to radio transmission section 25. Radio transmission section 25 transmits a transmission signal via antenna 11 after carrying out predetermined radio processing.
The communication apparatus of the reception side will be explained below. FIG. 2 is a block diagram shows a conventional communication apparatus.
The radio signal transmitted from the aforementioned communication apparatus is received through antenna 51 and subjected to predetermined radio processing in radio reception section 52. The received signal outputted from radio reception section 52 is separated into receiving signal and control signal in control signal separation section 53 and outputted to switch 54. Here, a control signal shows a transmission method selected in the transmission side.
Switch 54 outputs the receiving signal to either BPSK demodulator 56, QPSK demodulator 57, 8PSK demodulator 58, 16QAM demodulator 59 or 64QAM demodulator 60 according to the control signal.
BPSK demodulator 56, QPSK demodulator 57, 8PSK demodulator 58, 16QAM demodulator 59 and 64QAM demodulator 60 each demodulates the respective receiving signal and outputs the obtained received signal to switch 55.
Switch 55 outputs the receiving signal which is separated in control signal separation section 53 after being demodulated by either BPSK demodulator 56, QPSK demodulator 57, 8PSK demodulator 58, 16QAM demodulator 59 and 64QAM demodulator 60 to reception quality estimating section 61 and other external sections.
Reception quality estimating section 61 estimates reception quality of the receiving signal and outputs it to modulator 62. Modulator 62 modulates the transmission data and reception quality information and outputs the result as a transmission signal to radio transmission section 63. Radio transmission section 63 transmits a transmission signal via antenna 51 after carrying out predetermined radio processing.
Operation of the conventional communication apparatus will be explained below.
FIG. 3 is a table showing the correspondence relation between transmission method and control signal. FIG. 3 shows the correspondence relation between transmission method and control signal. Here, transmission method shows the modulation technique and control signal which is periodically transmitted to a communication partner.
When the signal is transmitted with BPSK modulation technique, communication apparatus 10 uses “000” as a control signal. When the signal is transmitted with QPSK modulation technique, communication apparatus 10 uses “001” as a control signal. When the signal is transmitted with 8PSK modulation technique, communication apparatus 10 uses “010” as a control signal. When the signal is transmitted with 16QAM modulation technique, communication apparatus 10 uses “011” as a control signal. Finally, when the signal is transmitted with 64QAM modulation technique, communication apparatus 10 uses “100” as a control signal.
FIG. 4 shows a transmission example of the control signal. In FIG. 4, the horizontal axis represents time. In addition, a1, a2, a3 and a4 each represents decision standard when transmission method determining section 15 determines the transmission method.
Here, when the channel quality is worse than a1, communication apparatus 10 transmits the signal with BPSK. When the channel quality is more than a1 and worse than a2, communication apparatus 10 transmits the signal with QPSK. When the channel quality is more than a2 and worse than a3, communication apparatus 10 transmits the signal with 8PSK. When the channel quality is more than a3 and worse than a4, communication apparatus 10 transmits the signal with 16QAM. Finally, when the channel quality is more than a4, communication apparatus 10 transmits the signal with 64QAM.
At time t1, since the channel quality estimated by channel quality estimating section 14 is more than a1 and worse than a2, transmission method determining section 15 determines the transmission of signal with QPSK, and based on the table in FIG. 3, control signal “001” corresponds to conventional QPSK is outputted.
At the time t2, since the channel quality estimated by channel quality estimating section 14 is worse than a1, transmission method determining section 15 determines the transmission of signal with BPSK, and based on the table in FIG. 3, control signal “000” corresponds to BPSK is outputted. Similar to time t2, at time t3 and t4, transmission method determining section 15, based on the table in FIG. 3, outputs control signal “000” corresponds to BPSK.
Similar to time t1, at time t5, t6 and t7, transmission method determining section 15, based on the table in FIG. 3, outputs control signal “001” corresponds to QPSK.
At time t8, since the channel quality estimated by channel quality estimating section 14 is more than a2 and worse than a3, transmission method determining section 15 determines the transmission of signal with 8PSK, and based on the table in FIG. 3, outputs control signal “010” corresponds to 8PSK. Similar to time t8, at time t9 and t10, transmission method determining section 15, based on the table in FIG. 3, outputs control signal “010” corresponds to 8PSK.
At time t11, since the channel quality estimated by channel quality estimating section 14 is more than a3 and worse than a4, transmission method determining section 15 determines the transmission of signal with 16QAM, and based on the table in FIG. 3, outputs control signal “011” corresponds to 16QAM. Similar to time t11, at time t12, t13, t14 and t15, transmission method determining section 15, based on the table in FIG. 3, outputs control signal “011” corresponds to 16QAM.
At time t16, since the channel quality estimated by channel quality estimating section 14 is more than a4, transmission method determining section 15 determines the transmission of signal with 64QAM, and based on the table in FIG. 3, outputs control signal “100”, corresponds to 64QAM. Similar to time t16, at time t17, transmission method determining section 15, based on the table in FIG. 3, outputs control signal “100” corresponds to 64QAM.
Accordingly, in the aforementioned adaptive modulation communication system, the communication apparatus of transmission side carries out transmission by updating adaptively modulation technique and carries out transmission after multiplexing modulation technique information such as (number of Multi-Level, etc.) in the transmission signal. Thus, the communication apparatus of reception side can perform demodulation based on modulation technique information even if the modulation technique is adaptively updated.
Moreover, there is a case where the information of the selected transmission method is not transmitted from the communication apparatus of transmission side, in such a case, the communication apparatus of reception side uses the so-called blind mode in which transmission method is estimated and then the received signal is demodulated.
FIG. 5 is a block diagram showing a configuration of a conventional communication apparatus using a blind mode. However, the sections similar to those shown in FIG. 2 are assigned the same reference numerals and explanation thereof will be omitted.
The communication apparatus of FIG. 5 comprises BPSK determining section 70, QPSK determining section 71, 8PSK determining section 72, 16QAM determining section 73, 64QAM determining section 74 and comparison section 75, a different point from the communication apparatus of FIG. 2 is that the demodulation is carried out after estimating the modulation technique of the received signal.
BPSK determining section 70 collects the phase distribution or amplitude distribution of a symbol pattern of the received signal, determines whether these distributions coincide with distribution of the BPSK symbol pattern and outputs the determination result to comparison section 75. QPSK determining section 71 collects the phase distribution or amplitude distribution of a symbol pattern of the received signal, determines whether these distributions coincide with distribution of the QPSK symbol pattern and outputs the determination result to comparison section 75. 8PSK determining section 72 collects the phase distribution or amplitude distribution of a symbol pattern of the received signal, determines whether these distributions coincide with distribution of the 8PSK symbol pattern and outputs the determination result to comparison section 75.
16QAM determining section 73 collects the phase distribution or amplitude distribution of a symbol pattern of the received signal, determines whether these distributions coincide with distribution of the 16QAM symbol pattern and outputs the determination result to comparison section 75. 64QAM determining section 74 collects the phase distribution or amplitude distribution of a symbol pattern of the received signal, determines whether these distributions coincide with distribution of the 64QAM symbol pattern and outputs the determination result to comparison section 75.
Comparison section 75 compares determination results outputted from BPSK determining section 70, QPSK determining section 71, 8PSK determining section 72, 16QAM determining section 73 and 64QAM determining section 74, and estimates the modulation method from the result in which the receiving signal symbol pattern is mostly coincide with a symbol pattern of each modulation technique. In addition, comparison section 75 carries out the switching between switch 54 and switch 55 from the estimating result of modulation method.
However, because the selected information shows the signal transmitted with a transmission technique which can be selected among all transmission techniques in the conventional apparatus is transmitted to a communication partner, the kinds of information of the selected transmission method increases and the data capacity used for distinguishing the information of such selected transmission method becomes large, hence, there is a problem that the capacity of the transmitting data increases further in every transmission unit.
Moreover, in blind mode in which a transmission method is estimated and reception processing is carried out in the reception side, there is a problem that a large number of calculations are required for estimation, or the error rate of estimation becomes large because there is a large number of candidates as an estimated transmission method.